Custom Site-Built ADU Builders
Some lots defeat a factory unit. A narrow side yard, a steep slope, no crane access, or a design that has to match a 1920s bungalow: that is when you want a contractor who frames the ADU in place. Site-built takes longer and the price moves with the design, but the floor plan is not fixed and nothing has to fit on a truck. This is the national page, covering the best custom builders in the markets that do not have their own page here, from Portland and Sacramento to Atlanta, Raleigh, Nashville, Boise and Florida. We rank on ADU volume, whether the framing and finish crews are in house, and how clearly permitting is priced.
- 1
Design-build ADU specialist in Portland, Oregon with 275+ units completed since 1997. Offers four distinctive model options and full custom construction services, from design through permitting to move-in.
- 2
Licensed Boise ADU contractor with 20+ years team experience, offering site-built ADU construction with fixed-price contracts and transparent cost breakdowns across the Treasure Valley.
- 3
Durham, North Carolina design-build contractor specializing in custom ADUs, garage conversions, and multigenerational homes. Licensed general contractor with 5-star Houzz and Google ratings.
- 4
A 15-year ADU specialist operating across Oregon and Washington with three design series (Traditional, Modern, and Urban) ranging from 357 to 1500+ square feet. Handles permits and utilities coordination as part of the build.
- 5
Sacramento-based ADU builder serving 100+ Northern California communities. Specializes in custom detached units, garage conversions, and design-build services with tech-driven estimates and permitting management.
- 6
Atlanta-based custom ADU builder offering detached units, attached units, garage conversions, and studio spaces with comprehensive in-house design, permitting, and construction management.
- 7
A Portland and Vancouver specialist that builds site-constructed ADUs from design through occupancy, with roots in 30+ years of custom home building. Transparent, all-in pricing and a typical 6–9 month timeline.
- 8
Award-winning California design-build firm with 15 years of experience, 3,500+ completed projects, specializing in custom ADUs, homes, and remodels across California and Washington.
- 9
Family-owned Sacramento-area contractor since 1997, specializing in full-service ADU design and construction for Northern California homeowners.
- 10
Charlotte-focused ADU specialists built on founder Bryan Alenky's deep expertise and obsessive attention to preconstruction planning, with emphasis on fixed pricing and reliable timelines.
- 11
Orlando-based site-built ADU specialist with 30+ years of experience, building concrete-block units across Florida with standardized models and custom options ranging from studios to two-bedroom units.
- 12
A 30-year design-build firm in Portland and Seattle with an extensive ADU portfolio spanning aging-in-place suites, rental units, and creative studios. Known for precision craftsmanship and modern building science.
- 13
Greenville-based design-build firm specializing in custom ADUs, additions, and luxury remodels with over 34 years of experience managing every step from permitting through final handover.
- 14
A Portland and Vancouver family business founded by cousins Scott Le and Jimmy Lam, offering new-build ADUs, garage conversions, and basement conversions across the Portland metro and SW Washington. Licensed and insured in both states.
- 15
Nashville-based family-owned builder since 1987, now in second generation, specializing in custom ADUs, remodels, and additions across Belle Meade, Franklin, Brentwood, and surrounding areas.
Frequently asked questions
When should I choose a site-built ADU instead of a pre-fabricated one?
You should choose site-built construction if your lot has a steep slope, a narrow side yard, or lacks crane access for a factory unit. This method is also better if you want a floor plan that isn't fixed or a design that must match the specific architectural style of your existing home.
How long does the construction process typically take for a site-built unit?
While timelines vary by builder, some specialists in this category report a typical timeline of 6 to 9 months from design through occupancy.
Can these builders help me with the permitting and utility coordination process?
Yes, many of the featured builders offer design-build services that include handling permits, utility coordination, and construction management. This allows them to manage the project from the initial design phase through to completion.
Are there builders who offer fixed pricing to help manage my budget?
Several contractors in our directory offer fixed-price contracts or transparent cost breakdowns to provide more predictability. This is especially helpful since the price of a site-built ADU often moves based on the complexity of your custom design.